While I had my engine apart, waiting for a replacement cylinder head, I made some modifications to the old factory (failed open) thermostat.

Before I took everything apart, I was running the in-line thermostat mod using a 195 deg t-stat inside a Meziere thermostat housing.
I got to thinking about the TDF custom thermostat housing and the benefits of a properly functioning bypass valve within the thermostat. How a failed factory thermostat combined with a 195 deg inline thermostat could cause coolant flow problems by not allowing coolant to bypass properly during engine warm-up.
Then I thought about how my old Ford 302 didn't have a bypass valve in its thermostat. The bypass was always wide open. Its bypass line was smaller than the outlet to the radiator. This way, when the thermostat opened, the larger path to the radiator became the path of least resistance and the majority of the coolant flowed through the radiator.
This old Ford engine was not unique. The vast majority of engines ever produced had their cooling systems and thermostat housings designed this way.
Why should this CRD engine be any different?

So what I did was I chiseled apart the old thermostat housing, disposed of the thermostat valve inside, put it back together and sealed it up with JB Weld.
During the process I accidentally broke off the small plastic elbow that was the "de-gas" line to the top of the coolant tank. I plugged and sealed it with JB Weld also.
This forced me to reroute my heater hoses.
What was the outlet to the heater is now the de-gas line to the top of the coolant tank.
What was the outlet from the drivers side of the head to the EGR cooler, is now running to the heater core. (EGR valve is completely deleted)
The bypass outlet at the bottom of the thermostat is still the bypass.
The heater core outlet is still the same.
Both the bypass and heater core outlets run to the water pump inlet just as they did from the factory.
The large outlet to the radiator in now wide open.

For the past 600 miles since getting my engine back together, I have been running with no thermostat whatsoever. Naturally, the engine runs very cool.
During my morning drive to work, 75 deg F ambient, the engine coolant temp runs between 130 and 140.
During my drive home in the afternoon, 90 deg F ambient, the engine coolant temp runs between 170 and 185 with the A/C on.
On one hot afternoon, while stuck in slow moving traffic, with A/C on, I saw coolant temp hit 198.
The thermostat housing and all hoses are tightly sealed. No sign of any coolant leaks and no loss of coolant from the tank.

I know that a cold running engine is not as efficient so I expect to see a slight drop in MPG.
Eventually I will put the in-line thermostat back in and I expect everything to function just as it did from the factory, if not better.

I'm not suggesting that this is the greatest new thing to do for your CRD.
I'm not saying that its in any way better than the TDF thermostat. (although it is much less expensive)
I just wanted to share my experiment with my fellow CRD owners and if any problems arise I will update accordingly.

(pictures)

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U.S. Army Retired

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U.S. Army Retired

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U.S. Army Retired

I wonder if you'll over heat in a high load situation do to the coolant moving through the system too quickly? Probably urban legend, but I heard that was possible a long time ago. If not, that might be a really good mod for equatorial regions.

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05 CRD: H.D.S2 stat,WW Ironrock trilink&LCA's, OX rear,ARB front, 4.10's, ARB bumper, Suncoast,OME 3.5, JBA UCA,rock rails, Moabs&265/75 Duratracs, GDE tunes ,FFD fan,ARP's, 2 micron fuel, new valves,sasquatch battery tray & grid heater, tensioner relocated
Mech fan, VH & AC delete

When I was a young hot rodder I had heard the same thing but could never confirm it.
I think good airflow is most important under high loads.
It doesn't matter what thermostat you have, if the engine temp gets above 210 and never comes back down, the engine will overheat.

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U.S. Army Retired

Yeah, with a mechanical fan you'll probably be good. I think the TDF thermostat will pay for itself with fuel savings, and less repairs, likewise with the GDE tune.

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05 CRD: H.D.S2 stat,WW Ironrock trilink&LCA's, OX rear,ARB front, 4.10's, ARB bumper, Suncoast,OME 3.5, JBA UCA,rock rails, Moabs&265/75 Duratracs, GDE tunes ,FFD fan,ARP's, 2 micron fuel, new valves,sasquatch battery tray & grid heater, tensioner relocated
Mech fan, VH & AC delete

flash7210:

I will try to explain why your method of fixing the cool running CRD engine and its poorly functioning thermostat assembly does NOT achieve the same results as a Hot Diesel Solutions Model 001 engine thermostat assembly....not even close. You made these claims in the following thread...

"Stant thermostat" viewtopic.php?f=5&t=83789

"Nothing against the HDS thermostat, it a great product, but there are other ways of accomplishing the same goal without spending $500.
I modified my factory t-stat housing and combined it with a Meziere in-line.
It may not be as nice looking as the HDS but it functions the same.
And I did it for under $100."

I CALL B.S. ON THIS... NO WAY DOES YOUR SET UP FUNCTION THE SAME WAY AS A MODEL 001.

My explanation will have to wait for a while as I am busy trying to ramp up for another production run.

Suffice it to say that NONE of my customers have had over heat issues attributed to the H.D.S. Model 001, but you yourself have reported high running temperatures with your set-up.

"Hayden HD Clutch and HDS 203F Tstat" viewtopic.php?f=5&t=85062&start=0

":roll:
Never truely overheated.
Just got hotter than I like. 225 max.
Only happened like 3 times in the last 2 years."

Way to bring up a year old thread Jeff. Please save your speech just this one time. We have all heard it plenty of times

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2005 Crd Silver Limited- arps, rockers, 7v etechno's, egr deleted, v6 airbox, metal cac's. Yeti's stage 2 tune. Euro TC, Ram tcm, pml transmission pan, facet lift pump

Are you a moderator, jws84_02? Did I break some kind of rule by bringing up an old thread?

If you are not, butt out... I am merely pointing out what flash7210 claims in his threads and posts, and what is really happening.

I have a right to post here, just like member joelukex4 has a right to post on the threads I start, like "ADD YOUR NAME HERE IF YOU WANT A NEW DESIGN THERMOSTAT".

viewtopic.php?f=169&t=75791

I thought the idea here on LOSTJEEPS was to get to the truth of the matter in regards to repairs and upgrades on our Jeeps.... However, according to you all that seems to matter regarding what is allowed on threads is if the member posting is aligned with your way of thinking.

What exactly are you trying to say with this post, anyway? This is the first opportunity I have had to post on flash7210's modified thermostat model.... you have most definitely not "heard it plenty of times".

If it seems I keep repeating myself it is because there are CRD owners who keep muddling with their engine cooling systems and making changes to it that the O.E. engineers never intended for this engine, and then encountering problems. People like joelukeX4 are continuing to use the in-line thermostat valve option and promote it as a viable solution, and then turning a blind eye to the problems they encounter. flash7210 is doing something similar with his modification, and I will be pointing out the shortcomings in his design as well.

If you have a problem with that, send an e-mail message to Heather and whine to her.

Yes, Gentlemen:

Running without a thermostat can apparently cause overheat conditions in some circumstances, for exactly the reason given by Mountainman. Here is a link that discusses the subject...

https://www.reddit.com/r/MechanicAdvice ... erheating/

I dont know if I believe that the reason too much flow is bad is because it doenst spend enough time in the radiator. a certain amount of air flowing over a radiator of a certain temperature must remove a certain amount of BTU's. There are equations for that. The only thing more flow would do is make it so the delta T of the coolant from one side of the radiator to the other lower which would make the average temp of the radiator hotter and make heat removal to the air GREATER. The total BTU/second would increase despite each individual mm^3 of coolant not dumping as much heat. That mm^3 of coolant is going to pump through the engine faster and get back to the radiator sooner. It would all equalize out and the coolant would end up at the same temp average temp. Each mm^3 of coolant would spend less time cooling in the radiator, but also less time heating in the engine.

The only way I could see lots of flow being a bad thing is if the flow becomes turbulent(vs laminar) inside of the engine or inside of the radiator and the heat transfer to the coolant from the engine and from the coolant to the radiator becomes less effective.

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2006 CRD - GTB2056 turbo by Dieselguy86, Eco Trans Tune, Lift Pump, Week's, HDS Tstat, Racor Filter, ARP's, OME 790's+Top Plate, JBA 2.5", JBA UCA, Moab's+265/75R16, ARB Bull Bar, 4.10's, TrueTracs

I probably should have never posted this a year ago.
Running without a thermostat is not a good idea.
I myself only ran like this for a couple weeks before putting my inline thermostat housing back in.
During the time that I did run without the thermostat the engine never overheated. And on typical FL summer afternoons never had problem reaching a operating temp of 190. It also never went above 200.

For other vehicles overheating from lack of thermostat, I don't know if it's increased coolant flow rate or not spending enough time in the radiator that causes it.
But I do know this, the thermostat regulates coolant flow through the engine.
Without a thermostat, coolant in the front most cylinders has a shorter path out to the radiator. Coolant in the rear most cylinders has a longer path.
Even though the head gasket is designed to control this flow difference by having smaller/fewer water jacket openings in the front cylinders, without a thermostat the front most cylinders will run cooler.
The thermostat regulates this flow/cooling difference by forcing all cylinders to heat up evenly. It then opens at the prescribed temperature to allow coolant flow out to the radiator.
The bypass opening/valve helps keep coolant circulating while the thermostat is closed and the engine is warming up.

The radiator fan activation temp, whether its electric or mechanical, should be closely matched to the thermostat opening temp (within 5-10 deg). This way, when operating under conditions with low airflow (low vehicle speed), the fan will pull air through the radiator and cool the coolant just as the thermostat opens. Once sufficiently cooled the thermostat closes and the cycle repeats.

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U.S. Army Retired

When the inline thermostat does open, is the bypass back into the engine still open? so will some coolant still recirculate and some go out to the radiator?

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2006 CRD - GTB2056 turbo by Dieselguy86, Eco Trans Tune, Lift Pump, Week's, HDS Tstat, Racor Filter, ARP's, OME 790's+Top Plate, JBA 2.5", JBA UCA, Moab's+265/75R16, ARB Bull Bar, 4.10's, TrueTracs

With my modified thermostat housing, yes.

Although in my case, this does not seem to be a problem. Afterall, when open, the outlet to the raditator is the path of least resistance.
My coolant temp sensor and cylinder head temp sensor indicate that the cooling system is working well.
The only time things got too hot (225F) was one hot afternoon in Atlanta during slow moving traffic. Turning the AC-off brought temps back down.
(previous too hot instances[2] were before the thermostat mod)

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U.S. Army Retired